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Optimized Gate Size for FET Random Logic

IP.com Disclosure Number: IPCOM000087147D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Elder, WH: AUTHOR [+2]

Abstract

A circuit parameter "gain" may be defined to provide a gate size which just meets the requirements of the driven circuit. The optimized gate size reduces gate area which saves chip space, gate capacitance and gives improved circuit densities which may be traded for increased wirability.

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Optimized Gate Size for FET Random Logic

A circuit parameter "gain" may be defined to provide a gate size which just meets the requirements of the driven circuit. The optimized gate size reduces gate area which saves chip space, gate capacitance and gives improved circuit densities which may be traded for increased wirability.

The gain of the driven circuit acts as a load on the circuit being designed. The gain may be related to down level which the circuit under design must deliver to support the fan-in of the driven circuits.

The figure shows a NOR circuit A under design that provides a down level to support the gain g(B) of the driven NOR circuit B.

While the NOR circuits A and B are shown as employing depletion loads, the present concept applies to linear and saturated load technologies as well. The gain definition also applies to NAND, AND/OR INVERT (AOI) and OR/AND INVERT (OAI) circuits. For a complex circuit configuration, gain is calculated by the following:

(Image Omitted)

Where W(a) is the gate width of the active device

L(a) is the gate length of the active device

W(1) is the gate width of the load device

L(1) is the gate length of the load device.

A method for optimizing the gate sizes of the sequence of field-effect transistors (FET) circuits begins, on a net basis, with the calculation of the gain for each circuit driven by the circuit under design and comparing the gains to determine the maximum value. The maximum gain determines the lowest down le...